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reviewing the water quality report

Posted by greentoe357 z7b Brooklyn NY (My Page) on
Wed, Jun 12, 13 at 12:00

I just checked out my local water characteristics here (http://www.nyc.gov/html/dep/pdf/wsstate12.pdf, page 10) for the first time ever. Wondering if I need to modify the potting mix recipes or fertilizer program (currently Foliage-Pro exclusively) in any way.

Our water is a bit too alkaline for plants (pH 6.7 to 9.2 with 7.2 average). BUT alkalinity is within the acceptable range at 11.2-19.3 mg/L CaCO3 with 14.8 average. Because alkalinity is low, I understand high pH does not matter and should not compel me to do anything differently in the soil mix or the fertilizer. Right?

Should I pay attention to any other metrics?


Follow-Up Postings:

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RE: reviewing the water quality report

Use white vinegar to lower your pH and hardness which increases nutrient uptake and lowers salt build up. Great advice for water like ours.


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RE: reviewing the water quality report

Phildeez, thanks. It's been a few weeks that I've been adding vinegar (2 tbsp per gallon) along with Foliage-Pro (1/4 teaspoon per gallon) at every watering. Hard to say if vinegar helps or hurts, as I've changed a bunch of cultural factors including the soil for many plants.

Generally, my understanding is that if water alkalinity is within acceptable range, then there is no need to lower a slightly elevated water pH. Can someone confirm my understanding? I do not think vinegar hurts though either - but if it does not help, then I'll be glad to simplify my life and skip it.


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RE: reviewing the water quality report

  • Posted by dsws none (My Page) on
    Wed, Sep 4, 13 at 10:18

I replied about alkalinity in the similar thread over in Houseplants forum: http://forums2.gardenweb.com/forums/load/houseplt/msg0901530213004.html?3914

Here is a link that might be useful: the other thread


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RE: reviewing the water quality report

Water PH is an indicator but not the end-all, be-all metric. Water alkalinity is much more important to know and has a bigger influence on your substrate PH and nutrient update.

My tap is 7.8 PH with 135ppm alkalinity. Over 120ppm is going to cause you substrate PH increase problems over the long haul. I think I read the sweet spot is 50-90ppm. So you take measures by injecting acid to bring it down. The PH also comes down under 7.0 to levels simulating acidic rain water.

Fro the record, Al irrigates with 8.8 PH water without issues really.


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RE: reviewing the water quality report

  • Posted by dsws none (My Page) on
    Wed, Sep 4, 13 at 19:04

Btw, ppm = mg/L, approximately.

Al fertilizes when he waters, so I suspect it's not at 8.8 when he waters with it.


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RE: reviewing the water quality report

>> My tap is 7.8 PH with 135ppm alkalinity. Over 120ppm is going to cause you substrate PH increase problems over the long haul. I think I read the sweet spot is 50-90ppm.

And if my water alkalinity is 15 on average, what practical implications for my plants does that have?


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RE: reviewing the water quality report

@DS - How many notches on the pH scale will a few drops of FP/gal lower hose water?

@GT - 15 what? Which measurement you using?


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RE: reviewing the water quality report

I was talking about alkalinity, which I think you were as well. It is from 11.2 to 19.3 mg/L CaCO3 with 14.8 average for my water.


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RE: reviewing the water quality report

I'm no expert on the conversions but isn't a 15 mg/L (are we saying that's 15 ppm?) close to rain water alkalinity? I have zero experience with low pH, low alkalinity, soft water situations. My tap may as well be liquid rock.

DS, been thinking more about your point of the effect of water-soluble fert on pH and alkalinity. How much does a weak dose of FP/gal affect/lower those stats? How long does it take? Does it expire/decay at some point and those stats rebound back up? Maybe somebody can chime in.


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RE: reviewing the water quality report

Tap water is buffered mainly by carbonate, which buffers in the range around 6.4. So even a tiny bit of anything acidic will drop the pH from 9 down to about neutral, just as it only took a tiny bit of extra alkali to bump it up to 9 once it was past neutral. That's why it has that range.

I don't know what the pH of foliage pro (or any other fertilizer) actually is. You could formulate a fertilizer with the same NPK numbers at almost any pH.

But the phosphate in fertilizer (the concentrate or crystals) is measured in percent, whereas alkalinity of water is measured in parts per million. There are three teaspoons in a tablespoon, 16 tablespoons in a cup, and 16 cups in a gallon. So teaspoon per gallon is one part in 768. Let's say you're putting in a bit less than a teaspoon so that we can call it one part per thousand, for round numbers. Then each percent of acidic material (after adjusting for the different molecular weight, so it's in CaCO3 equivalent units) would be a percent of a part per thousand: ten parts per million.

This rough order of magnitude fits with Oxboy's rule of thumb that 120 ppm is enough to worry about.

--

None of the stuff in tap water or fertilizer that affects pH will decay particularly quickly. Eventually something might metabolize the nitrogen, and CO2 from the air will turn into carbonate in an alkaline solution. But for the most part, as soon as you mix the stuff it's at the pH it will be at.

This post was edited by dsws on Thu, Sep 5, 13 at 12:24


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RE: reviewing the water quality report

So, I ordered and received these pH test strips: http://www.williamsbrewing.com/40-to-70-pH-TEST-STRIPS--P1001.aspx. Today is watering day, so I got ready to test. Wanted to test plain water (I let mine off-gas for a few days), then water + fertilizer, then if pH is high, gradually adding vinegar while continuing to test.

Here is what I got:

Tap water, off-gassed for 6 days: pH 5.5.
With 1/4 teaspoon per gallon Foliage-Pro 9-3-6 added: pH 5.3.

So... Looks like experiment is over. No need to add vinegar, as this is within the perfect pH range for most houseplants.

Anything I am missing?

I'll repeat the test at next watering just to see how consistent the results are, but for now that's what I got.


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RE: reviewing the water quality report

  • Posted by dsws none (My Page) on
    Tue, Sep 17, 13 at 10:39

You could try checking the pH of your water before the long exposure to air, just for curiosity.


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RE: reviewing the water quality report

GT, did you ever repeat the test?

I reread what you were doing up in the thread, and if your irrigation alkalinity was really 15ppm (i.e., rain or distilled water), then a tablespoon of vinegar would've essentially turned your gallon of water into...a gallon of vinegar. Deadly of course for your planties.

I tested a newly-opened gallon of distilled and got 6.5 pH. Immediately adding 1/4 tsp of FP dropped it down to 6.3 so that's in keeping with your experiment results.

I'm switching to distilled permanently for all my indoor plants and I'm running through a series of exercises to make sure the zero alkalinity water isn't crashing my 5-1-1 substrate pH to dangerously low levels. My goal is to get both irrigation water and soil pH in the ballpark of 6.0....and more or less learn what it takes to keep it around there.

I figure with liming and my tap water on the basic side and FP, peat, composting bark and distilled water on the acid side, I have enough tools available to get to the stability I need.


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RE: reviewing the water quality report

>> GT, did you ever repeat the test?

Yes, twice. And within a point more or less, I got the same results.

>> I reread what you were doing up in the thread, and if your irrigation alkalinity was really 15ppm (i.e., rain or distilled water), then a tablespoon of vinegar would've essentially turned your gallon of water into...a gallon of vinegar. Deadly of course for your planties.

Ummmm... I do not know what to tell you, except (1) I do not understand how I'd get a gallon of vinegar (is the vinegar effect SOOOOOO strong on distilled water?), but more importantly (2) that I am just a dummy who had read somewhere online that adding vinegar was beneficial to house plants, and so I was doing that because Internet is never wrong. :-)

My plants survived "the vinegar era" just fine - despite the vinegar or because of it, I guess we'll never know. They actually got even better during that time, but that may be because Foliage Pro and a grow light and I think a better soil mix were all introduced roughly at the same time.

There is another wrinkle that I do not feel comfortable with. The muni report says pH is 6.7 to 9.2 with 7.2 average, but my result was 5.5. Yes, the report is from 2012, and they measure water in the reservoirs (I think), but I measure it off the tap and after about a week of off-gassing. Still, the difference is suspicious and leads me to wonder how reliable those little pH strips are.

In fact, if I understand this correctly, both my inconsistency with the muni water report and your question howcome I did not kill my plants can both be explained by inaccurately lower readings of my pH testing strips.

For now (since those tests), with the info I have, I turned off the vinegar spigot.


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RE: reviewing the water quality report

Adding vinegar is good to bring down high alkalinity. If I used my tap water of 135ppm to irrigate pots, I'd acidify with vinegar.

I'm not convinced I have your water alkalinity figured out. I'm a moron when it comes to the conversions. It could be you're a rare case of low pH and high alkalinity.


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